This work reports a Mg (130 nm)/Al (50 nm) bilayer to realize high-reflectivity ohmic contact for n-GaN. The contact resistivity of $3.75\times 10 ^{ {-4}} \Omega \cdot $ cm $^{ {2}}$ with Mg/Al contact was achieved after annealing at 250 °C in ambient Ar for 1 min. The specific contact resistivity was found to change moderately when the annealing temperature was below 400 °C, but the ohmic characteristics deteriorated significantly when the annealing temperature was above 450 °C. X-ray photoemission spectroscopy revealed that the Ga 3d (Ga-N) peak decreased by 0.28 eV with the increase of the annealing temperature from 250 to 450 °C, which can increase the metal-semiconductor contact barrier height, leading to deteriorated current-voltage characteristics. The reflectivity of the samples was found to decrease with the increase of the annealing temperature, and decreased greatly when the temperature exceeded 350 °C. When the annealing temperature is below 300 °C, the reflectivities of the samples are greater than 90% for wavelengths from 350 to 550 nm. Mg/Al is therefore a promising candidate to serve as a reflective n-GaN electrode for GaN-based flip-chip LEDs to improve the light extraction efficiency.

中文翻译：

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n-GaN上的高反射率Mg / Al欧姆接触

这项工作报道了一个Mg（130 nm）/ Al（50 nm）双层，可实现n-GaN的高反射欧姆接触。的接触电阻率 $ 3.75 \ times 10 ^ {{-4}} \ Omega \ cdot $ 厘米 $ ^ {{2}} $ 在250°C的环境Ar中退火1分钟后，与Mg / Al的接触得以实现。发现当退火温度低于400℃时，比接触电阻率适度变化，但是当退火温度高于450℃时，欧姆特性显着劣化。X射线光电子能谱显示，随着退火温度从250到450°C的升高，Ga 3d（Ga-N）峰降低了0.28 eV，这可能会增加金属-半导体接触势垒的高度，从而导致电流-电压特性。发现样品的反射率随退火温度的升高而降低，而当温度超过350℃时其反射率则大大降低。当退火温度低于300°C时，对于350至550 nm的波长，样品的反射率大于90％。因此，Mg / Al是用作GaN基倒装芯片LED的反射n-GaN电极以提高光提取效率的有希望的候选者。